The present invention relates to novel plant promoters and their uses. More particularly, the present invention relates to tissue specific and constitutive plant promoters, expression constructs containing same and plants expressing structural genes or antisense polynucleotides under the control of any of the novel promoters. The invention further relates to methods of identifying minimal functional plant promoter region derived from the novel plant promoters.
The selection of a promoter in the engineering of a heterologous gene expression construct is oftentimes a critical factor in obtaining adequate expression of the desired gene. Promoters are typically found at the 5′ upstream regions of coding sequences of genes and are typically directly or indirectly recognized and bound by DNA-dependent RNA polymerases during the initiation of transcription of the coding sequence. Consequently, promoters play a major role in regulating gene expression. There are several general classes of promoters used in the genetic engineering of plants: (i) tissue or organ specific promoters; (ii) developmental stage specific promoters; (iii) inducible promoters; and (iii) constitutive promoters. It will be appreciated that a single promoter may be categorized into more than a single category.
Tissue specific or organ specific promoters drive gene expression in a certain tissue such as in the kernel, root, leaf or tapetum of the plant. Chemical or environmental stimuli such as heat, cold, wounding, infection (e.g., viral, bacterial or fungal infection) and other stress conditions, induce inducible promoters. Although tissue specific and inducible promoters are required for certain applications, constitutive promoters are the most widely used promoters in the transgenic plants industry.
Tissue and developmental stage specific promoters derive the expression of genes, which are expressed in particular tissues or at particular time periods during plant development. Tissue-specific promoters are valuable tools as they permit specific expression of heterologous genes in a tissue and/or developmental stage selective manner, indicating expression of the heterologous gene differentially at a various organs, tissues and/or times, but not in other. Constitutive promoters are defined as those promoters which are capable of driving high levels of gene expression in most or all of the tissues of a plant. Constitutive promoters are useful, for example, for producing herbicide tolerant plants and for many other applications. Presently, the most widely used constitutive promoter in the genetic engineering of plants is the CaMV35S promoter (which is of a viral origin); other widely used constitutive promoters include the maize polyubiquitin promoter and the rice actin promoter.
In general, those familiar with the art agree that constitutive promoters that drive a high level of heterologous gene expression in most of the tissues of a plant are only a few in number and are of considerable value in the field of genetic engineering of crop plants.
It is well recognized among art scholars that there is a widely recognized need for, and it would be highly advantageous to have, novel tissue specific and constitutive plant promoters.